1. Field of the Invention
Embodiments of the present invention generally relate to a method and apparatus for measuring AC voltages.
2. Description of the Related Art
In today's quest for obtaining energy from renewable resources, solar power is becoming an increasingly desirable option. Photovoltaic (PV) modules utilized in solar power systems convert energy from sunlight received into direct current (DC). The PV modules cannot store the electrical energy they produce, so the energy must either be dispersed to an energy storage system, such as a battery or pumped hydroelectricity storage, or dispersed by a load. One option to use the energy produced is to employ one or more inverters to convert the DC current into an alternating current (AC) and couple the AC current to the commercial power grid.
PV power inverters coupled to the commercial power grid must constantly monitor the voltage of the Utility Power (grid) at the inverter location to comply with relevant Underwriters Laboratories (UL) and Institute of Electrical and Electronic Engineers (IEEE) standards, in particular UL-1741 ed. 1 “Standard for Inverters, Converters, Controllers and Interconnection System Equipment for Use with Distributed Energy Resources”, May 1999, and IEEE 1547-2003 “IEEE Standard for Interconnecting Distributed Resources with Electric Power Systems”. Additionally, other devices that may be coupled to the grid, such as uninterruptable power supplies (UPS), must also monitor the grid power and comply with certain isolation standards.
In monitoring the grid, each phase of the grid voltage must be monitored and measured separately. Traditionally, grid monitoring circuits utilize transformers to isolate and step-down the grid voltages before sampling the AC voltage on each phase of the grid. Such transformers are bulky, heavy, and expensive. Additionally, these transformers continuously consume power and may exhibit distortion problems.
Therefore, there is a need for a method and apparatus to efficiently measure AC voltages.